Problem: Stephanie is 4 times as old as Umaima and is also 12 years older than Umaima. How old is Umaima?
Solution: We can use the given information to write down two equations that describe the ages of Stephanie and Umaima. Let Stephanie's current age be $s$ and Umaima's current age be $u$ $s = 4u$ $s = u + 12$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $u$ , and both of our equations have $s$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4u$ $-$ $ (u + 12)$ which combines the information about $u$ from both of our original equations. Solving for $u$ , we get: $3 u = 12$ $u = 4$.